The
Eurasian (or European) otter population of western Europe underwent a
widespread decline
during the 20th century. The decline, and subsequent recovery, has been
well documented in the UK, although less historical information is available
for most other countries.

The situation in Europe
was reviewed during the period of decline, showing that otters were rare
or extinct in much of central Europe in a broad band extending from Italy
across to central Spain in the south up to Sweden and southern Norway.
'Widespread' populations existed mainly in western areas (Portugal, Ireland,
Scotland, and parts of Spain, France, Wales and England) or eastern areas
(from Finland through to Greece).

A recent review found
evidence of a recovery. This showed that, although European populations
were still considered healthy and widespread in only a third of the 37
countries for which data were available, the number where they were believed
to be increasing had gone up from 28% to 38%. The proportion where otters
were believed to be threatened, declining, very rare or extinct had gone
down from 40% to 22%.

There was a sudden
and widespread decline in the success of otter hunts throughout much of
England and Wales in 1978, which corresponded closely with a perceived
decline in the otter population from the mid 1950s. This was similar to
changes observed in populations of various species of predatory birds
and mammals and probably had the same cause - the introduction of cyclodiene
pesticides (dieldrin and related compounds) in the mid-1950s. These pesticides
were withdrawn from use in the UK in the 1970s.

Since 1977, as a result
of a series of national otter surveys, substantial parts of England, Wales
and Scotland have been surveyed three times, Ireland once and parts of
it twice. In England and Ireland alternate 50 km squares were searched,
in Wales and Scotland the whole land area was covered. These surveys involved
recording the presence or absence of otter signs (usually their faeces,
known as spraints) according to a protocol which has been widely used
in Europe. In addition, the coast of the Shetland Islands has been surveyed
twice by a different method involving the counting of active otter holts.
Spraint surveys only provide information on distribution, while the holt
surveys, which can only be used in certain coastal areas, provided estimates
of the population.